1. Field of the Invention
The present invention relates to a cleaning process, and more particularly, to a cleaning process which is simplified and in which a time required for the cleaning process is reduced. The process has an excellent cleaning effect.
2. Description of the Related Art
In a semiconductor wafer manufacturing process, a photoresist (PR) layer should be formed on a semiconductor substrate and removed after a predetermined process. The process of removing the photoresist (PR) layer is referred to as a cleaning process. The cleaning process can be performed after a variety of operations of the semiconductor wafer manufacturing process, such as a front end of the line (FEOL) operation, a back end of the line (BEOL) operation or ion implantation. The cleaning process is a process in which contaminants, such as a photoresist or photoresist residues, are removed from a surface of a substrate in a ultra-fine pattern. To this end, a wet cleaning process using water and various solvents and a dry cleaning process using supercritical carbon dioxide (CO2) have been developed.
In a conventional wet cleaning method including an RCA method, a cleaning process can be properly performed for purposes. However, many problems exist in that the conventional wet cleaning method is not suitable for manufacture of an ultra large scale integrated circuit (ULSI). For example, in a wet cleaning process, wettability of cleaning fluid to a fine structure having a high aspect ratio is lowered, and due to repeated rinsing and drying processes, unwanted particles are generated. In addition, there are problems concerning metal inadvertently contaminated by a liquid-phase chemical solution, water marks and corrosion, costs for ultra-pure purification and high purity purification of chemicals. Process equipment clusterization is not easily performed because of the large size of equipment and complicated process. In addition, there are problems with environmental contamination caused by waste water and waste fluid and costs for treating waste water.
In addition, since a large quantity of chemical solvent is used in a conventional RCA cleaning method, problems exist in that a wafer may be damaged and a photoresist layer may not be completely removed. To address the problems, new solvent has been developed. However, in the conventional wet cleaning process, due to a characteristic of the molecular structure of cleaning fluid, molecules of the cleaning fluid cannot easily infiltrate an ultra-fine structure less than 65 nm. In particular, it is not easy to clean copper for manufacturing a high performance semiconductor in a next generation fine pattern having a low-K dielectric layer material.
To address the problems, the development of plasma, gaseous or supercritical dry cleaning technology is needed. However, when a photoresist is removed using an oxygen plasma ashing method used in a dry cleaning process, a wafer is damaged and contaminated by oxygen plasma, and due to the existence of contaminants, an additional wet cleaning process needs to be performed. In addition, damages due to a wet method or a plasma dry cleaning process do not occur in a cleaning process using the oxidation action of ozone that has been recently developed. However, problems such as environmental contamination caused by ozone exist.
During semiconductor manufacture, processes such as dry etching or wet etching, ashing or ion implantation are performed, and photoresist may remain on a wafer. Accordingly, conventionally, a partial drying process and a wet process, that is, two processes such as ashing and organic strip processes, are performed to remove the photoresist and thus, the number of processes is increased, resources are consumed and numerous costs for waste water treatment are needed.
In addition, when wet cleaning is accompanied as described above, an additional drying process, such as spin drying, isopropyl alcohol (IPA) vapor drying, or marangoni drying, is needed. In these drying methods, water marks are left and strain is generated and the possibility of recontamination caused by an electrostatic force is high. In particular, in the case of IPA vapor drying, a high temperature (greater than 200° C.) for IPA vaporization should be maintained and a large amount of IPA is required.
A semiconductor wafer cleaning method using a supercritical process in which supercritical CO2 and several common solvent are mixed has been already introduced. However, because a homogeneous transparent phase cannot be formed by simply mixing polar common solvent with supercritical nonpolar CO2, problems concerning the conventional wet cleaning process are not solved and cleaning efficiency is low. Even though a homogeneous transparent phase supercritical state is formed, a temperature greater than 100° C. and a pressure greater than 300 bar are needed and thus, costs are increased. To address these problems, even when a surfactant is introduced, an additional mixer or a ultrasonic device is needed so as to form a supercritical homogeneous transparent phase and thus, manufacturing time is increased.
In addition, high purity (greater than 99.99%) CO2 is used to manufacture a semiconductor. In the prior art, an efficient purification process of purifying and recovering used CO2 to reuse CO2 cannot be performed.